1. Field of the Invention
The present invention relates to the treatment of a waste water stream containing water, oil, sand, oily sand and gas to separate the oil, sand, gas and water out of the waste water stream. In particular, the present invention is related to a method and apparatus for use on offshore and onshore oil and gas well drilling operations whereby the water and sand can be purified to a point at which it can be released into the environment without damaging the enviornment.
2. Description of the Prior Art
Most oil and gas wells both onshore and offshore produce a large amount of waste water which commonly contains oil, gas and sand. The sand contained in the waste water stream frequently is contaminated or soaked with oil to the extent that the sand cannot be discharged into the environment because of the environmentally dangerous levels of oil contained in the sand. Most state and federal regulations now require that waste water and sand discharge into the environment meet certain maximum limitations on the amount of oil contained therein.
Numerous methods have been proposed for treatment of waste water streams for removal of pollution therefrom. Typical of these methods are the following:
U.S. Pat. No. 4,198,300 discloses an apparatus for removing suspended oil droplets from water, including a vertical pipe suspended from an offshore oil platform partially submerged in the sea surrounding the platform, a means for injecting a waste water stream into the middle portion of the pipe and a means for injecting gas into the lower portion of the pipe and for diffusing the gas to disperse the gas into gas bubbles, so that the gas bubbles counter currently contact the waste water stream as the gas bubbles rise to the upper portion of the pipe, thereby attaching the oil droplets and reducing the overall density of the oil droplets efficiently so that the upper velocity of the oil droplets is greater of the downward velocity of the waste water stream and promoting the separation of oil droplets from the waste water stream, and means for withdrawing the oil droplets from the upper portion of the pipe. The apparatus uses natural gas air or inner gas as the gas medium for forming the gas bubbles.
U.S. Pat. No. 4,221,671 discloses an upright circular tube settler with stacked tube modules for removal of solids from fluids and for removal of one fluid from another. The tube modules are for use in a tube settler of the type having vertically disposed concentric tubular walls. The modules contained concentric rows of essentially straight fluid flow passages open at both ends, the passages in each row of a particular model being tilted relative to the vertical in the same direction and to substantially the same degree, the passages in each row being skewed in relation to other passages in the same row of the same tier. The passages cooperate to provide means for directing fluid in a substantially spiral path around a tank.
U.S. Pat. No. 4,217,211 discloses a sewage treatment process wherein sewage is passed into deep underground shaft and is improved by passing a liquor of the sewage in the underground shaft through an inner shaft which extends only part way down into the underground shaft. A mixing shaft and liquor nozzles are provided for receipt of the sewage liquor passing downwardly. The action of the descending liquor through the nozzles entrains ascending liquor from the shaft into the descending liquor resulting in recirculation which allows extended contact time of the liquor with a microorganisms used to digest the sewage.
U.S. Pat. No. 4,186,087 discloses a method and apparatus for separating substances from liquids by flotation using bubbles comprising absorbing a substance present in a liquid on bubbles, floating the bubbles absorbing the substances and separating the substance from the bubbles, characterized by allowing the bubbles absorbing the substance to ascend through a fluid route in a tube independent of the ambient turbulently flowing liquid and then collecting and separating the substance from the liquid at the upper end of the tube. The apparatus includes a vertical column provided at the bottom with a gas-diffusing means and a tube placed inside the vertical column, the tube being provided with a means for collecting bubbles at the lower end and concentrating in the collected bubbles at the upper end.
U.S. Pat. No. 4,066,540 comprises a vertical column for continuous froth flotation having therein a froth separator, a raw water inlet pipe, a treated water discharge pipe and gas dispersing unit, and stepped shelves disposed inside the column and adapted to provide thorough contact between the bubbles and water subjected to treatment.
U.S. Pat. No. Re. 28,378 discloses an apparatus for effecting purification of liquids by flotation wherein a mixture of gas in liquid is subjected to sufficient pressure for the gas to dissolve in the liquid and to form a solution of the gas in the liquid. The solution is introduced into a flotation tank and pressure is lowered to form gas bubbles in the tank at a slow rate, thereby forming very small bubbles. The slow rate at which the very small gas bubbles are formed provides purification of polluted liquids by flotation.
U.S. Pat. No. 3,893,918 discloses a method for separating materials leaving a well including utilizing an elongated separator conduit partially above and below the surface of a body of water to establish a fluid column in the water, supplying an oil containing fluid mixture in the fluid column and causing the fluid to float downwardly through a flowing zone over a plurality of baffle means to induce coalescent separation of oil from fluid, intermittently interrupting the supply of fluid to impede the downward velocity of fluid for a time sufficient for oil to rise from the flowing zones into the quiescent zones defined by the baffles, flowing oil accumulated in the quiescent zones upwardly to establish an upper layer of oil in the fluid column, flowing oil accumulated in the lower quiescent zones through the upper quiescent zones, withdrawing oil from the upper oil layer, and flowing the oil free liquid from the exit zone of the separator from the body of water beneath the surface thereof.
U.S. Pat. No. 3,520,415 discloses a separation vessel disposed in a vertical column for separating a hydrocarbon material from a slurry of water, bitumen, and sand. The vessel includes a impeller mechanism, a sand settling zone, and a froth disengaging zone. A set of turbulence reducing baffles is mounted between the underwash sparger and the froth withdrawal conduit.
U.S. Pat. No. 2,806,599 discloses a vacuum control for gravity separators utilized for effectively recovering extremely fine fractions of sand suspended in water utilizing a low pressure cyclone gravity separator whereby fluids are spiraled about in a cyclone in a circular manner to separate solids such as sand from the fluids.
U.S. Pat. No. 2,754,980 discloses a fluid separator for separating solids or liquid particles from fluids. The separator is disposed in a vertical manner and contains no moving parts. The fluid is helically whirled in a stream so that the particles become centrifugally concentrated in the outer peripheral regions of the stream, the fluid stream opening tangentially into the upper end of a vertical casing, a well inside with the lower end open to the interior of the casing and upper open exterior of the casing, means in the well for impressing a helical path upon the fluids stream passing from the bottom to the top of the well, and an ejector zone intermediately at the end of the well.
U.S. Pat. No. 1,869,241 discloses a vertical apparatus for the separation of the solid substances, such as for separating the graphite from its ore by the emulsion process. The fluids flows through a central pipe and into a series of baffles to effect separation of solids from the fluid.
U.S. Pat. No. 1,458,805 discloses an apparatus for the settlement of solid particles in suspension in liquids and discloses a vertical column having a series of baffles therein, and a number of parallel sloping settling surfaces separated by similar settling spaces to separate particles from a liquid stream flowing therethrough.
U.S. Pat. No. 3,359,357 discloses a process and apparatus for refining hydrocarbons which includes a vertical column having an inclined spiral plate over which the fluids are flowed.
The above patents disclosed various separation and flow treatment devices but none show the novel combination of elements provided for separating oil, gas, sand and water in a waste water stream disclosed in the present invention.